Use of c02 evolution rate for the study and control of fermentation.

Stassi, P., Rice, J.F., Munroe, J.H. and Chicoye, E.

Abstract
Measurement of C02 evolution rate (CER) has been used to study, monitor and control multiple lager fermentations on the laboratory scale. C02 was measured throughout fermentation using thermal mass flow meters (TMF) selected for their ability to give a true measure of mass without the need to compensate for pressure or temperature. The TMF's, each with a range suited to the vessel size and/or process conditions were connected to a data acquisition and control system (DACS). The DACS coupled with the appropriate software was able to monitor the output of sensors for pH, temperature, pressure, dissolved oxygen etc., as well as control the fermentation process. CER was shown to correlate with specific gravity, the extent of yeast growth and the pH minimum during fermentation and with the S02 concentration in beer at the end of fermentation so that it was possible to estimate these parameters without the need for off-line measurements. A process control loop was used to control the CER at a fixed setpoint temperature. The equipment and techniques used to monitor and control CER are described for laboratory fermentations. The concept can be easily applied to the monitoring and control of production lager fermentations. As fermentations are lengthy the sampling rate permits a number of fermentations to share the same flow meter. Currently the sampling rate is one CER measurement/hour but it is likely that this could be reduced to one CER measurement in 2 hours without compromising the data.
Keywords : beer carbon dioxide control fermentation growth pH process sulphur dioxide yeast